In the completion of oil wells which traverse earth formations, inflatable packers have been used for a considerable period of time. An inflatable packer typically has a central, longitudinally extending tubular or casing member on which is disposed a tubular elastomer or inflatable packer member. The tubular elastomer member is typically attached or sealed with respect to collars at both of its ends. One of the collars, for example, the lower collar has passage means including valves which control the input of fluid from the interior of the tubular member to the interior of the tubular elastomer member. While the passage means and valves need not be in a collar, they are generally located at or near a collar. When the fluid pressure within the tubular member is increased sufficiently to open an inflate valve in the passage means, the packer element begins to inflate. As the packer element inflates, the fluid that occupies the annulus between the packer element and the well bore is displaced. The fluid in the annulus may, (1) move upward displacing excess fluid from the casing well bore annulus, (2) move downward and enter permeable intervals below the packer, (3) enter permeable intervals adjacent to the packer, (4) initiate and flow into fractures adjacent to or below the packer and/or, (5) become trapped in borehole irregularities preventing complete inflation of the packer.
Since the inflation fluid in long packers is typically cement, upward movement of the displaced fluid is highly desirable as it would: (1) allow for complete unhampered inflation of the packer and (2) minimize the risk of well damage that is often associated with the other displacement modes. Unfortunately this upward displacement of fluid may be hampered by irregular inflation of the packer. For example, inflation of the top of the packer element will prevent upward movement of the displaced fluid. Alternatively, the packer element could inflate in a random manner along its length and trap fluid in the well bore along the sections of the packer element that inflate more slowly.
Attempts to minimize this problem of irregular packer inflation have included placement of the passage means (the inflation entry point of fluid) at the bottom of the packer element. However, this frequently fails because variations in the properties of the inflatable packer element along its length are the dominate factor in determining the section or sections of the packer element that inflate first.